Design of laser system for Subaru LGS AO

We present the development status of the laser system for Subaru Laser Guide Star Adaptive Optics System. We are manufacturing the quasi-continuous-wave sum frequency laser as a prototype. The optical efficiency of sum frequency generation normalized by the mode-locked fundamental YAG (1064 nn) laser output power is achieved to be 14 using the non-linear crystal, periodically poled potassium titanyl phosphate (PPKTP). Output power at sodium D2 line was about 260 mW. The optical relay fiber and the laser launching telescope are also described in this paper. For the optical relay fiber, we are testing an index guided photonic crystal fiber (PCF), whose core material is filled by fused silica, and whose clad has close-packed air holes in two dimension. The coupling efficiency was evaluated as about 80 % using 1mW He-Ne laser. We introduce the design of laser launching telescope (LLT), which is a copy of VLT laser launching telescope, and the interface to the Subaru Telescope.